This invention relates to electromagnetic valves and particularly to an electromagnetic proportional valve.
The invention concerns an electromagnetic proportional valve with at least one solenoid and an armature displaceable in its field which acts on at least one restrictor, where this restrictor is located in a channel in which a pressure can be built up in a fluid stream fed in, in particular a magnetic valve for generating a control pressure that is dependent on an electric signal, preferably for regulating a multiway valve or a pump capable of swinging out in two directions through the neutral position and/or the motor of a hydrostatic drive unit.
Electromagnetic valves for generating a control pressure have been known to date, in which case a coil acts on an armature, which in turn acts on a restrictor. The magnetic force generally acts here against the force of a spring. The restrictor can be formed on the edges of a slide valve supported against the spring or the restrictor can be formed at the mouth of a borehole, in which case a "baffle plate" is pressed against the mouth with the force generated by the armature, so that the throttling action is more intense, the greater the magnetic force. A stream that is either prescribed by the delivery stream of a pump or is limited by a nonadjustable restrictor is fed here to the restrictor and by varying the restrictor influenced by the armature the pressure head in front of it is modified and this pressure head is used as a signal or the pressure of the oil buildup is used as the control pressure, which acts, for example, in regulating a pump either on the pilot of a servo follow-up control power amplification device or acts directly on the servo piston of the pump. If the pump is moveable through the neutral position, the control pressure has to act at will on one of the two sides of the servo piston. For this purpose, it is conceivable to provide a reversing valve in the control pressure line that conveys the control pressure to the side of the servo piston that is to be regulated. However, it is customary in this case to provide two electromagnetic valves, one of which is regulated and thus generates a control pressure in the assigned control pressure line, which acts on the corresponding side of the servo piston, while the other magnetic valve remains unaffected and consequently leaves the restrictor fully open, with the result that there is no pressure on the side of the servo piston assigned to this restrictor. Such an arrangement is very expensive with respect to both production cost and the structural space required. There is also the danger in valves in which the throttling action is produced on the edge of a slide valve that the slide valve becomes jammed, e.g., as the result of a dirt particle, so that the slide valve remains in its regulated position even if no more field is induced in the coil of the magnet. In this case it is impossible to return the pump to the zero-stroke position, or it is possible only if just as large a pressure is applied to the second side of the servo piston and thus an equilibrium of the control pressures is produced, with the further danger that if the slide valve released suddenly, only the additionally applied control pressure acts and the pump shoots into a position that is not desired at all.
It is also known to have the two armatures act, each through a push rod on each an arm to a two-arm lever, which is in turn connected with a third lever arm with the slide valve that is capable of moving in two directions.
The invention proposes an electromagnetic valve of the above type, which facilitates building up a desired control pressure in one of two selectively regulatable pressure channels, preferably control pressure channels, at a low construction cost, and also eliminating the said disadvantages.
This goal is accomplished by the combination of the following features:
(a) Two spools are located in a common housing and they act in one direction on a single common armature body, in which case two restrictors located one on each side of this one armature body are assigned to it.
(b) Each restrictor is designed as a seat valve.
The statement that an integrated armature body is present does not exclude the fact that this armature body is not uniform and has a contraction approximately in the middle, and does not exclude the fact that this one armature body is comprised of two or more work pieces.
The seat valve can be designed as a ball valve, but also as any other known type of seat valve.
Through the implementation form a relatively small valve for two selectively regulatable control pressures is offered, which due to its compact form is suitable for incorporation as a "building block" in an "assembly of prefabricated machine parts" on pumps or multiway valves, e.g., block control devices of various types and sizes. The pumps or multiway valves that are provided for remote hydraulic control through a control pressure can be used unchanged or with only slight changes, where now instead of a hydraulic signal, an electric signal is sent to the valve or pump and the electric signal is converted at the pump into a fluidpressure signal proportional to the electric signal.
The implementation form also has various advantages:
When the armature hangs up in an actuation direction, opposite force can be exerted by applying an electric voltage to the other coil, which draws the magnet toward the neutral position. This magnetic force acts in addition to the force that results in the restrictor designed as a seat valve as a result of the pressure built up in front of it. The operational reliability is increased through this possibility of intervention or the possibility of back-regulation when there is a seizing of the moving parts of the control mechanism.
Since the force of the electromagnet acts on a small-dimension seat valve, the use of very small forces along with a high operating reliability is possible. It is thus possible to get along with very weak electric signals, i.e. very small electric currents.
The use of seat valves also has advantages over the use of throttling at the edges of an axially displaceable slide valve inasmuch as the danger of seizing is eliminated or at least substantially reduced and a force is generated directly on the seat valve body and acts against the force of the electromagnet so that an additional spring is not required. During counter-control in the case of seizing, this force acts together with the magnetic force.
Through the use of the "building block" offered by the invention it is possible to retain the design of pumps and multiway valves with remote hydraulic control without substantial change, i.e., no mechanical answer-back signal of the pump swing angle or of the displacement position of the piston of the multiway valve is necessary. In this manner, a simple expansion of hydraulically adjustable units to electrical control is possible by flanging on the valve according to the invention.